Problem: Complete the recursive formula of the geometric sequence $-125\,,-25\,,-5\,,-1,...$. $b(1)=$
The first term is $-125$ and the common ratio is $\dfrac15$. ${\times\dfrac15\,\curvearrowright}$ ${\times\dfrac15\,\curvearrowright}$ ${\times\dfrac15\,\curvearrowright}$ $-125,$ $-25,$ $-5,$ $-1,...$ This is the recursive formula of $-125\,,-25\,,-5\,,-1,...$. $\begin{cases} b(1)=-125 \\\\ b(n)=b(n-1)\cdot\dfrac15 \end{cases}$